The Chilean tsunami and how it affected the East Coast of Aus.

12 Mar 2010 0 Share

Figure 1. The Southport Jetty (Tasmania) tide gauge showing the arrival of the tsunami. The red line is the actual tide level, the blue line, right of  00:00 hours the impact of the tsunami (source: Bureau of Meteorology)

Figure 1. The Southport Jetty (Tasmania) tide gauge showing the arrival of the tsunami. The red line is the actual tide level, the blue line, right of 00:00 hours the impact of the tsunami (source: Bureau of Meteorology)

Story by | Professor Andy Short

The February 28 Chilean tsunami did make it all the way to eastern Australia some 15 hours after the devastating 8.8 magnitude earthquake. Many, like me, went to coastal vantage points or grabbed their surfboards and waited to see what eventuated. As we all know – not much.

I was surfing at Seal Rocks when the Easter 1964 Alaskan tsunami reached the east coast, and there we did see a noticeable change in the exposure of the rocks on the point, at the time not knowing we were surfing a tsunami. This tsunami was 30 cm high when it reached the coast and so the wave was just detectable as the water level rose and fell by that amount over a period of a few minutes. However the Chilean tsunami which generated devastating waves up to 2.5 m high along parts of the Chilean coast, was only 10 cm high when it reached the east coast of Australia.

The reason for the low height is due to two things. First, the initial tsunami was not that big at 2.5 m, compared to over 10 m for the Boxing Day Aceh tsunami; and second, it has to travel a long way to get here, 10,000 km and in the process detour around New Zealand, so that by the time it reached our shore it had been greatly diminished. The Southport (Tasmania) tide gauge shows the impact of the tsunami when it arrived at low tide about 1 am on 28 February. It caused oscillation in the water level of about 10 to 20 cm, which lasted for a few hours

Figure 2.	Arrival of the Chilean tsunami at various New Zealand locations.

Figure 2. Arrival of the Chilean tsunami at various New Zealand locations.

Figure 3. Chilean tsunami arriving at Santa Barbara, California. Red line is tide record, green line the tsunami which reached over 1 m at 00:00 hours.

Figure 3. Chilean tsunami arriving at Santa Barbara, California. Red line is tide record, green line the tsunami which reached over 1 m at 00:00 hours.

The tsunami was higher in New Zealand where it reached up to 1.5 m at Gisborne and on the Chatham Island (Figure 2), and it was even bigger on the west coast of North America where it reached over a 1 m at Santa Barbara (Figure 3).

Figure 4. 	Surfer translated wave height and period at Snapper Rocks at the time of arrival of the Chilean tsunami (source: Coastalwatch.com).

Figure 4. Surfer translated wave height and period at Snapper Rocks at the time of arrival of the Chilean tsunami (source: Coastalwatch.com).

Coastwatch was also looking out for the tsunami with its dozens of beach video cameras along the east coast. However because of the small size of the waves it was not detectable to the cameras or the naked eye. Up at the Quicksilver Pro on the Gold Coast the contest was postponed owing to the marine warning. The Coastalwatch camera at the site was using the latest technology from CoastalCOMS WavePak software to record the wave height and period during the arrival of the tsunami at around 9am. As shown in Figure 4 the WavePak software recorded a slight increase in wave period and a small peak in wave height around 9am. It cannot be confirmed definitely if this was caused by the Tsunami reaching the Australian coastline but it was recorded at the Snapper camera site. To read more about the CoastalCOMS Wave Pack software please visit www.coastalcoms.com.

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